How to test the battery on Xiaomi Mi 9T: a complete guide with tests and tips

The Xiaomi Mi 9T (aka Redmi K20 in some regions) is one of the brand’s most popular smartphones, but over time, even its capacious 4,000 mAh battery starts to lose capacity. If your phone runs too fast, overheats or suddenly shuts down when it’s 20 to 30 percent, the problem is likely to be in the battery. In this article, we’ll look at all the available ways to test the battery, from standard MIUI tools to professional tests with ADB and third-party apps.

It's important to understand that lithium polymer batteries degrade over time, and after 300 to 500 charging cycles, their capacity can decrease by 20 to 30 percent. However, it's not always the battery itself that is to blame: sometimes the problem is background processes, a faulty charger or even firmware, and we can help identify the true cause and give recommendations on how to extend the life of the battery or understand that it is time to replace it.

1. Checking the battery with hidden engineering code ##4636##

The fastest way to get basic battery information is to use the Android Engineering Menu, which is available on all Xiaomi smartphones, including the Mi 9T, and does not require any additional apps to be installed.

To open the menu:

1. Open the Phone app.
2. Enter the combination: ##4636## (no spaces).
3. In the window that appears, select Battery Information.

In this section you will see the following key parameters:

• 🔋 Level of charge (level) – current percentage in digital form.
• 🔌 Power source – shows whether the phone is connected to charging (AC — network adapter, USB — computer).
• 🌡️ Temperature: Normal values from 25°C to 40°C when charging. If the temperature is above 45°C, it's a sign of overheating.
• ⚡ Voltage: Must be between 3.7 and 4.3 V for lithium polymer batteries, values below 3.5 V or above 4.4 V indicate a malfunction.

⚠️ Warning: If the battery voltage drops below 3.4V at 10-15% charge, this may indicate severe wear or malfunction of the controller.

This method only gives instantaneous metrics, but it doesn't show real capacity or wear. For a deeper diagnosis, move on to the following.

2.Use of the AccuBattery application for detailed diagnosis

AccuBattery is one of the best battery health monitoring apps that analyzes charging cycles, measures actual capacity, and predicts wear and tear, and is available for free on Google Play.

After installation:

1. Open the app and provide all the necessary permissions (access to battery statistics and notifications).
2. Connect the phone to charging and wait for the full charging cycle (preferably 1-2 times).
3. Go to the Health tab to see the current battery capacity in milliamp hours (mAh).

What you can learn from AccuBattery:

• 📊 Real capacity - compare with the factory (4000 mAh for Mi) 9T). If the difference is greater than 20%, the battery is severely worn out.
• 🔄 The number of charging cycles, the more, the more wear and tear, and after 500 cycles, the capacity usually drops by 30 to 40%.
• ⚡ Charging/discharge speed – if the phone is discharged faster than 10% per hour in standby mode, there is a problem.
• 📉 Wear graph shows how capacity has decreased over time.

Example: if AccuBattery is 3200 mAh instead of 4,000 mAh, it means that the battery has lost 20% of its capacity, and then you should consider replacing it.

Charge the phone to 100% | Discharge to 5-10% without recharging |Repeat the cycle 2-3 times | Check the indicators in the Health tab-->

The critical threshold for replacing the battery on Xiaomi Mi 9T is a drop in capacity below 2800-3,000 mAh. At such values, the smartphone will discharge in 3-4 hours even with minimal load.

Verification through ADB (for experienced users)

If you want to get the most accurate data on the battery, you can use the Android Debug Bridge (ADB) tool, which requires connecting the phone to a computer, but gives you access to hidden parameters that don't show the application.

Instructions:

1. Download and install ADB Tools on your computer.
2. Turn on the Xiaomi Mi 9T developer mode: go to Settings → About Phone → MIUI version and press 7 times on this item.
3. Return to Settings → Additional → For developers and enable USB debugging.
4. Connect the phone to your computer and type in the command line:

adb shell


dumpsys battery

In response, you will receive detailed information including:

Notice the charge counter, which is the actual residual capacity, for example, if you have a value of 3.2 million, you have a 20 percent battery run-down.

⚠️ Attention: If in response ADB parameter of health OVER_VOLTAGE, UNSPECIFIED_FAILURE or COLD, This indicates a critical malfunction, and then the battery needs to be replaced as soon as possible, and it can fail at any time.

4. battery test via CPU-Z application

CPU-Z is a well-known iron diagnostics app that also shows battery information, and its advantage is that it doesn't require long calibration like AccuBattery, and it gives you a snapshot of the state.

How to use:

1. Download CPU-Z from Google Play.
2. Open the app and go to the Battery tab.
3. Pay attention to the fields Level, Voltage, Temperature and Health.

What can I find out:

• 📱 Wear level – some versions display as a percentage (e.g. Health: 85% means 15% loss).
• 🔋 Battery technology for Mi 9T Li-polymer should be indicated.
• 🔌 Charging/discharge current – if the current is less than 1000 mA when charging, the power supply or cable may be faulty.

CPU-Z is useful for quick checks, but it doesn't provide as detailed statistics as AccuBattery. It's better paired with other methods.

💡

If the Health field doesn't show up in CPU-Z, try restarting your phone or updating your app. Sometimes the data doesn't show up until after the full charge-discharge cycle.

5. Visual inspection and physical signs of wear

It doesn't always take software to figure out that there's something wrong with the battery.The physical symptoms often speak for themselves. 9T for the following signs:

• 🔥 Bloating - if the back cover or screen starts to "go away", it is a dangerous signal. The battery could swell due to overheating or short circuit.
• 🌡️ Excessive heating – if the phone heats up to 50°C and higher in normal use (not in games), this is a sign of battery degradation.
• ⚡ Sudden shutdowns – if the smartphone turns off at 20-30% charge, the battery controller gives incorrect readings.
• 🔌 Slow charging – if the phone charges from 0 to 100% longer than 3 hours, the battery or charging port may fail.

If you notice bloating, immediately disconnect the phone from charging and do not use it. The bloated battery can damage the screen or even ignite, in which case an urgent replacement at the service center is required.

Also pay attention to the Autonomous work:

• 📵 Normal wear: with moderate use (social networks, messengers), the phone holds 5-6 hours of screen.
• ⚠️ Average wear: the screen lasts 3-4 hours – capacity fell by 30-40%.
• ❌ Strong wear: discharge in 1-2 hours - battery on the verge of failure.

💡

If the Xiaomi Mi 9T discharges 1% in 1-2 minutes on standby, it almost always indicates a hardware malfunction of the battery, not a software bug.

6. Check through the MIUI service menu (hidden tests)

Xiaomi hides a service menu in the firmware where you can run iron tests, including the battery, which does not work on all versions of MIUI, but it is worth a try.

Instructions:

1. Open the Phone app.
2. Enter the code: ##6484## (for battery test) or ##64663## (full service menu).
3. If the code works, select Battery Test or similar.
4. Wait for the test to be completed – it usually takes 1-2 minutes.

In the test results, pay attention to:

• 🔋 Status – Must be Good or Normal.
• ⚡ Voltage – as in the engineering menu, should be within 3.7-4.3 V.
• 📊 Capacity – if any, compare with the factory 4000 mAh.

If the service menu doesn't open, your version of MIUI doesn't support it, in which case, use the other methods in this article.

7.When is it time to change the battery to Xiaomi Mi 9T?

Even if tests show wear and tear, it doesn't always require immediate replacement, and here are the specific criteria when you should consider replacing your battery:

If you decide to replace the battery, contact the official service center Xiaomi or checked repair. the cost of replacing the battery with the Mi 9T in 2026 is approximately 2000-3500 rubles (depending on the region and type of battery).

⚠️ WARNING: If you replace the battery yourself, you risk damaging the plumes or power controller. Xiaomi Mi 9T has adhesive battery attachment, and its sloppy extraction can lead to short circuit.

FAQ: Frequent questions about the Xiaomi Mi battery 9T